The present invention relates to an arrangement for contactless measurement of the rotational speed of a component arranged on a shaft with several revolving magnets in whose magnetic fields a stationary pulse wire sensor is arranged.
Such a measuring arrangement is known from practice, in which a pulse wire sensor is activated by the magnetic fields of several magnets which are arranged on the circumference of a rotating component. A pulse is triggered when the components of the magnetic fields parallel to the sensor exceed a certain minimum value.
According to the known laws of induction moving magnetic fields generate in their vicinity in conducting surfaces a changing magnetic flux which generates eddy currents. Similar to mechanical bearing friction such eddy currents represent an electrical stray current.
In certain applications, the eddy currents have a disruptive effect. For example, with turbine gas flowmeters there is only a very small driving torque to rotate the metering wheel at minimum flow. Therefore, the eddy currents lead to measuring errors in the lower measuring range.
Therefore, the object of the present invention was to develop a measuring arrangement of the aforementioned type which provides reliable measurements irrespective of the rotational speed, particularly in the lower measuring range.